Due to the shortage of fossil energy, countries around the world are aware of the importance of the environmental protection. In recent years, alternative energy and renewable energy technologies are developed, wherein the photovoltaic cell gets much attention. The photovoltaic cell directly converts solar energy into electrical energy. When the amount of the sunlight is greater and the concentration magnification of the concentrator module is higher, the electricity per unit area of the photovoltaic cell is higher and the cost of power generation of the photovoltaic cell is cheaper.
The conversion efficiency of the photovoltaic cells differs when that material of the photovoltaic cells changes. For example, the conversion efficiency of a silicon-based photovoltaic cell is about 12%˜20%, and the conversion efficiency of a group III-V based photovoltaic cell is about 31%˜41%. The silicon material absorbs energy having wavelength between 400 nm and 1100 nm, and the group III-V material absorbs energy having wavelength between 300 nm and 1900 nm. The conversion efficiency of the group III-V based photoelectric cell is higher compared with the silicon-based photovoltaic cell.
The concentrated photovoltaic cell generates power by focusing the sunlight on the group III-V based photovoltaic cell through optical concentrator so the power generation efficiency of the photovoltaic cell is increased and the cost of the power generation is reduced. Taking a photovoltaic cell having a size of 4 inches wafer and comprising group III-V based material for example, it can produce 2.4 W power under one sun without the optical concentrator and 650 W power under 500 suns with the optical concentrator. In this case, the concentration magnification of the optical concentrator is expressed with multiples of sun. For example, 500 suns expressed that the light intensity received by the photovoltaic cell with the optical concentrator is 500 times of that without the optical concentrator under the same unit area.
FIG. 1 illustrates a diagram of a conventional concentrator module 1. The concentrator module 1 comprises a first optical concentrator 13, a second optical concentrator 11 and a photovoltaic cell 10. FIG. 2 illustrates a top-viewed diagram of the photovoltaic cell 10. The photovoltaic cell 10 comprises a plurality of collector electrodes 102 and a plurality of grid electrodes 103 formed on an upper surface 101. FIG. 2A illustrates a partial enlargement of a top-viewed diagram of the plurality of grid electrodes 103. Each of the plurality of grid electrodes 103 comprises a same width w, and a spacing s between adjacent grid electrodes 103 is the same. A pitch d between the first grid electrode 103a and the second grid electrode 103b is the sum of the width w and the spacing s. As shown in FIG. 2A, the pitch d between the plurality of grid electrodes 103 is the same.
The first optical concentrator 13 and the second optical concentrator 11 focuses a sunlight 12 on the upper surface 101 of the photovoltaic cell 10 with high concentration magnification, which achieves higher photoelectric conversion efficiency, provides higher power generation and reduces the costs of power generation. However, the light concentration of the conventional concentrator module 1 is uneven. When the sunlight 12 is incident on the upper surface 101 of the photovoltaic cell 10, the light intensity distribution of the sunlight 12 is uneven on the upper surface 101, which leads to higher resistance of the photovoltaic cell 10 and reduces the power generation efficiency of the photovoltaic cell 10 as a whole. FIG. 3 illustrates an example of the conventional photovoltaic cell 10 with the conventional concentrator module 1. FIG. 3 shows an example of the photovoltaic cell 10 having a size 5 mm×5 mm. The photovoltaic cell 10 receives the sunlight 12 from the concentrator module 1. Within a radius of 1 mm from the center of the upper surface 101 of the photovoltaic cell 10, the concentration magnification of the sunlight 12 incident on the photovoltaic cell 10 by the first optical concentrator 13 and the second optical concentrator 11 is more than 1000 suns. Beyond a radius of 1 mm from the center of the upper surface 101 of the photovoltaic cell 10, the concentration magnification of the sunlight 12 incident on the photovoltaic cell 10 by the first optical concentrator 13 and the second optical concentrator 11 is less than 200 suns.